(none)
Balloon angioplasty, or the technology of reshaping of a blood vessel for the purpose of establishing vessel patency using a balloon tipped catheter, has been known since the late 1970""s. The procedure involves the use of a balloon catheter that is guided by means of a guidewire through a guiding catheter to the target lesion or vessel blockage. The balloon typically is equipped with one or more marker bands that allow the interventionalist to visualize the position of the balloon in reference to the lesion with the aid of fluoroscopy. Once in place, i.e., centered with the lesion, the balloon is inflated with a biocompatible fluid, and pressurized to the appropriate pressure to allow the vessel to open.
Typical procedures are completed with balloon inflation pressures between 8 and 12 atmospheres. A percentage of lesions, typically heavily calcified lesions, require much higher balloon inflation pressures, e.g., upward of 20 atmospheres. At times, the balloon inflation procedure is repeated several times before the lesion or blockage will yield. The placement of stents after angioplasty has become popular as it reduces the rate of restenosis.
Restenosis refers to the renarrowing of the vascular lumen following vascular intervention such as a balloon angioplasty procedure or stent insertion. Restenosis is clinically defined as a greater than 50% loss of initial lumen diameter. The mechanism or root causes of restenosis are still not fully understood. The causes are multifactorial, and are partly the result of the injury caused by the balloon angioplasty procedure and stent placement. With the advent of stents, restenosis rates have dropped from over 30% to 10-20%. Recently, the use and effectiveness of low-dose radiation administered intravascularly following angioplasty is being evaluated as a method to alter the DNA or RNA of an affected vessel""s cells in the hope of reducing cell proliferation.
Another cardiological malady is atrial fibrillation. Atrial fibrillation refers to very rapid irregular contractions of the atria of the heart resulting in a lack of synchronization between the heartbeat and the pulse. The irregular contractions are due to irregular electrical activity that originates in the area of the pulmonary veins. A proposed device, currently under development, for treating atrial fibrillation is a balloon filled with saline that can be ultrasonically agitated and heated. This device is inserted in the femoral vein and snaked into the right atrium. The device is then poked through the interatrial septum and into the left atrium, where it is then angled into the volume adjoining the suspect pulmonary vein with the left atrium.
Research in atrial fibrillation indicates that substantially complete circumferential necrosis is required for a therapeutic benefit. The above technique is disadvantageous in that circumferential portions of the tissue, desired to be necrosed, are not in fact affected. Other techniques, including RF ablation, are similarly inefficient. Moreover, these techniques leave the necrosed portions with jagged edges, i.e., there is poor demarcation between the healthy and the necrosed tissue. These edges can then cause electrical short circuits, and associated electrical irregularities, due to the high electric fields associated with jagged edges of a conductive medium.
The above technique is also disadvantageous in that heating is employed. Heating is associated with several problems, including increased coagulum and thrombus formation, leading to emboli. Heating also stimulates stenosis of the vein. Finally, since tissues can only safely be heated to temperatures of less than or about 75xc2x0 C.-85xc2x0 C. due to charring and tissue rupture secondary to steam formation. The thermal gradient thus induced is fairly minimal, leading to a limited heat transfer. Moreover, since heating causes tissues to become less adherent to the adjacent heat transfer element, the tissue contact with the heat transfer element is also reduced, further decreasing the heat transfer.
Another disadvantage that may arise during either cooling or heating results from the imperfections of the surface of the tissue at or adjacent to the point of contact with the cryoballoon (in the case of cooling). In particular, surface features of the tissue may affect the local geometry such that portions of the balloon attain a better contact, and thus a better conductive heat transfer, with the tissue. Such portions may be more likely to achieve cell necrosis than other portions. As noted above, incomplete circumferential necrosis is often deleterious in treating atrial fibrillation and may well be further deleterious due to the necessity of future treatments. Accordingly, a method and device to achieve better conductive heat transfer between tissue to be ablated and an ablation balloon is needed.
The present invention provides an enhanced method and device to inhibit or reduce the rate of restenosis following angioplasty or stent placement. The invention is similar to placing an ice pack on a sore or overstrained muscle for a period of time to minimize or inhibit the bio-chemical events responsible for an associated inflammatory response. An embodiment of the invention generally involves placing a balloon-tipped catheter in the area treated or opened through balloon angioplasty immediately following angioplasty. A so-called xe2x80x9ccryoplastyxe2x80x9d balloon, which can have a dual balloon structure, may be delivered through a guiding catheter and over a guidewire already in place from a balloon angioplasty. The dual balloon structure has benefits described below and also allows for a more robust design. The balloon is porous so that an amount of ablation fluid is delivered to the tissue at the ablation site.
The balloon may be centered in the recently opened vessel with the aid of radio opaque marker bands, indicating the xe2x80x9cworking lengthxe2x80x9d of the balloon. In choosing a working length, it is important to note that typical lesions may have a size on the order of 2-3 cm. In the dual balloon design, biocompatible heat transfer fluid, which may contain contrast media, may be infused through the space between the dual balloons. While this fluid does not circulate in this embodiment, once it is chilled or even frozen by thermal contact with a cooling fluid, it will stay sufficiently cold for therapeutic purposes. Subsequently, a biocompatible cooling fluid with a temperature between about, e.g., xe2x88x9240xc2x0 C. and xe2x88x9260xc2x0 C., may be injected into the interior of the inner balloon, and circulated through a supply lumen and a return lumen. The fluid exits the supply lumen through a skive in the lumen, and returns to the refrigeration unit via another skive and the return lumen.
The biocompatible cooling fluid chills the biocompatible heat transfer fluid between the dual balloons to a therapeutic temperature between about, e.g., 0xc2x0 C. and xe2x88x9250xc2x0 C. The chilled heat transfer fluid between the dual balloons transfers thermal energy through the balloon wall and into the adjacent intimal vascular tissue for the appropriate therapeutic length of time.
To aid in conduction, a small portion of the chilled heat transfer fluid between the dual balloons may contact the adjacent intimal vascular tissue for the appropriate therapeutic length of time due to the porosity or microporosity of the outer balloon.
Upon completion of the therapy, the circulation of the biocompatible cooling fluid is stopped, and the remaining heat transfer fluid between the dual balloons withdrawn through the annular space. Both balloons may be collapsed by means of causing a soft vacuum in the lumens. Once collapsed, the cryoplasty catheter may be withdrawn from the treated site and patient through the guiding catheter.
In more detail, in one aspect, the invention is directed to a device to treat tissue, including an outer tube, an inner tube disposed at least partially within the outer tube, and a dual balloon including an inner balloon and an outer balloon, the inner balloon coupled to the inner tube at a proximal and at a distal end, the outer balloon coupled to the inner tube at a distal end and to the outer tube at a proximal end. A first interior volume is defined between the outer balloon and the inner balloon in fluid communication with an inlet in the volume between the outer tube and the inner tube. The outer balloon is porous so that an amount of ablation fluid may be delivered to the ablation site.
Variations of the invention may include one or more of the following. The inner tube may further define a guidewire lumen, a supply lumen, and a return lumen. The supply lumen may define a hole or skive such that a fluid flowing in the supply lumen may be caused to flow into a volume defined by the inner balloon, and the return lumen may define a hole or skive such that a fluid flowing in a volume defined by the inner balloon may be caused to flow into the return lumen. The guidewire lumen may extend from a proximal end of the inner tube to a distal end of the inner tube. The device may further comprise at least two radially extending tabs disposed around a circumference of the inner tube to substantially center the inner tube within the dual balloon. The device may further comprise at least one marker band disposed on the inner tube to locate a working region of the device at a desired location. The device may further comprise a source of chilled fluid having a supply tube and a return tube, the supply tube coupled in fluid communication to the supply lumen and the return tube coupled in fluid communication to the return lumen. A source of fluid may also be included, the source of fluid coupled in fluid communication to a volume between the inner balloon and the outer balloon. The fluid may be a perfluorocarbon such as Galden fluid. The fluid may also include contrast media. The size of the pores of the outer balloon may be in the micron range, so long as the pores do not prevent the balloon from achieving a pressure of about 1 to 2 atmospheres. The pores may be disposed in one of a variety of shapes, including a band, a helix, and so on. The use of just a single pore may be employed as well to minimize fluid loss while still allowing some conduction enhancement.
In another aspect, the invention is directed to a method of reducing restenosis after angioplasty in a blood vessel. The method includes inserting a catheter into a blood vessel, the catheter having a balloon. The balloon is then inflated with a perfluorocarbon such that an exterior surface of the balloon is in contact with at least a partial inner perimeter of the blood vessel, the perfluorocarbon having a temperature in the range of about xe2x88x9210xc2x0 C. to xe2x88x9250xc2x0 C. The balloon is porous so that an amount of ablation fluid is delivered to the ablation site.
Variations of the method may include one or more of the following. The method may include disposing the catheter at a desired location using at least one radio opaque marker band. The method may include flowing the perfluorocarbon into the balloon using a supply lumen and exhausting the remaining perfluorocarbon from the balloon using a return lumen. The balloon may be a dual balloon, and the method may further include providing a heat transfer fluid in the volume between the dual balloons. The heat transfer fluid may include a contrast media fluid. The method may include disposing the catheter such that at least a portion of the balloon is in a coronary artery or in a carotid artery. The size of the pores of the balloon may be in the micron range, so long as the pores are not so large or multitudinous so as to prevent the balloon from achieving a pressure of at least about 1 to 2 atmospheres. The pores may be disposed in one of the variety of shapes disclosed above, including just a single pore.
In yet another aspect, the invention is directed to a method of reducing atrial fibrillation. The method includes inserting a catheter at least partially into the heart, the catheter having a balloon, a portion of the balloon located in the left atrium and a portion of the balloon located in a pulmonary vein. The balloon is porous so that an amount of ablation fluid is delivered to the ablation site. The balloon is inflated with a perfluorocarbon such that an exterior surface of the balloon, as well as a small portion of the ablation fluid, is in contact with at least a partial circumference of the portion of the pulmonary vein adjacent the left atrium, the perfluorocarbon having a temperature in the range of about xe2x88x9210xc2x0 C. to xe2x88x9250xc2x0 C.
Variations of the method may include one or more of the following. The balloon may have a working region having a length of between about 5 mm and 10 mm. The method may further include inserting a wire having a needle point from the femoral vein into the right atrium and forming a hole using the needle point in the interatrial septum between the right atrium and the left atrium. A guide catheter may then be inserted into the right atrium. A guide wire may further be inserted through the guide catheter into the right atrium and further into a pulmonary vein. The catheter may then be disposed over the guidewire into a volume defined by the joint of the right atrium and the pulmonary vein. The size of the pores of the outer balloon may be in the micron range, so long as the pores do not prevent the balloon from achieving a pressure of about 1 to 2 atmospheres. The pores may be disposed in one of a variety of shapes, including a band, a helix, and so on. The use of just a single pore may be employed as well to minimize fluid loss while still allowing some conduction enhancement.
Advantages of the invention may include one or more of the following. The invention inhibits or reduces the rate of restenosis following a balloon angioplasty or any other type of vascular intervention. At least the following portions of the vascular anatomy can benefit from such a procedure: the abdominal aorta (following a stent or graft placement), the coronary arteries (following PTCA or rotational artherectomy), the carotid arteries (following an angioplasty or stent placement), as well as the larger peripheral arteries.
When the invention is used to treat atrial fibrillation, the following advantages inure. The cooled tissue is adherent to the heat transfer element and/or to the ablative fluid, increasing the heat transfer effected. Since very cold temperatures may be employed, the temperature gradient can be quite large, increasing the heat transfer rate. The ablative fluid that passes from the balloon to the tissue may assist the heat transfer conduction and the ensuing cell necrosis.
In both embodiments, heat transfer does not occur primarily or at all by vaporization of a liquid, thus eliminating a potential cause of bubbles in the body. Nor does cooling occur primarily or at all by a pressure change across a restriction or orifice, this simplifying the structure of the device. Thrombus formation and charring, associated with prior techniques, are minimized or eliminated.
Additional advantages will be apparent from the description that follows, including the drawings and claims.